1. Field of the Invention
The present invention relates generally to the field of imaging, and, more particularly, to an accelerated texture-based fusion renderer.
2. Description of the Related Art
Modern medical technology provides different modalities for acquiring 3D data, such as computed tomography (“CT”), magnetic resonance imaging (“MRI”), positron emission tomography (“PET”), and ultrasound. The information obtained from different modalities is usually complementary; for example, CT provides structural information while PET provides functional information. Thus, it is generally desirable to fuse multiple volumetric datasets.
FIG. 1 presents a sample fused image where functional data from PET is correlated with structural information from CT. FIG. 1 shows a sample fused rendering. The image on the left (FIG. 1(a)) shows structural information derived from a 512×512×512×12-bit CT dataset, while the image in the center (FIG. 1(b)) shows functional information derived from a 256×256×256×16-bit dataset PET dataset. The image on the right (FIG. 1(c)) is a simple fusion of the CT and PET datasets correlating structural and functional information. The “negatives” of each of the images is shown to facilitate printed reproduction.
Most existing fusion renderers require that all volumes be aligned and have the same resolution, thereby necessitating that all volumes be re-sampled except the one that is treated as the reference volume. The reference volume generally refers to the volume with the finest resolution to avoid losing information—the other volumes are re-sampled according to the grid of the reference volume. The reference volume may need to be expanded to fill the bounding box enclosing all volumes. The aggregate bounding box of the ensemble of volumes can be significantly larger than individual bounding boxes when the orientation of a volume happens to lie near the diagonal of another volume. The number of voxels after re-sampling is proportional to the volume of the aggregate bounding box. Therefore, re-sampling can significantly increase the processing time (both initially and for each rendering) as well as the amount of memory required.
The volumes usually need to be registered because different scanners can have different coordinate systems (in terms of origins and orientations). During registration all volumes, except the reference volume, are referred to as floating volumes. Various transformations, such as rotation, translation, scaling, and shearing, are applied to the floating volumes so that their features match those in the reference volume. Furthermore, re-sampling must be performed again after such a transformation. Registration typically requires user interaction, with visual feedback, that is repeatedly applied to refine the registration. The resample-based fusion render cannot response quickly enough for such requirements.